1. Field of Invention
The present invention relates generally to mufflers, and more particularly to mufflers that attenuate low frequency noise generated at the gas intake of compressors, internal combustion engines and other machines that produce noise during the process of taking in air or other gases.
2. Brief Description of Related Art
Machines such as air compressors and internal combustion engines--especially diesel engines--produce high level pulsations at multiples of the machine's rotational frequency range. Mufflers used to reduce intake pulsation noise generally are dissipative or reactive or a combination of the two. To be effective at low frequencies (i.e., below about 500 Hz) and over a broad frequency range, these types of mufflers must be very large and heavy. Most reciprocating compressors generally have first order pulsation frequencies in the 7 to 20 Hz range and produce significant intake noise at multiples of the pulsation frequency up to frequencies in the 300-400 Hz range. However, even large mufflers can generally only attenuate tones by less than about 6 dB below about 30 Hz. To compensate for such low frequency deficiencies, tuned filters may be designed for the low frequencies. However, the tuned filters are effective only over a very limited frequency range.